Fungi are critical organisms in the recycling of organic matter in nature. Fungi hydrolyze their organic surrounding habitat by producing extra cellular enzymes that they excrete into their surroundings. The enzymes produced by fungi are specific to the species of fungi and the substrate (food source) on which they grow. The environmental conditions present, i.e., the food sources available to the organism, induce the production of the specific enzymes required to catalyze the release of soluble nutrients from the organic matter in the organism's surroundings which can then be absorbed through the fungal cell walls and used by the organism for biosynthesis.
There are estimated to be over 1.5 million species of fungi with approximately 100,000 having been identified. The primary industrial use of fungi is the production of enzymes and fermented foods. Two species in particular are industrial workhorses: Trichoderma reesei and Aspergillus niger. However, literally thousands of fungi occupy the same ecological niche as Trichoderma and Aspergillus as decomposers and recyclers of cellulosic biomass and as yet have not been exploited commercially. The use of these organisms has co-developed with industrial fermentation technologies relying on submerged fermentation reactors and simplified liquid culture media. In most cases these organisms have been genetically manipulated to grow under liquid fermentation conditions and have been engineered to synthesize specific enzymes when stimulated by specific soluble inducing agents. However, the vast majority of fungi are aerobic organisms that cannot survive in an anaerobic condition or thrive in an aerobic submerged condition and whose enzyme expression is triggered by exposure to a natural, complex solid biologic substrates as a food source.
Solid state fermentation of fungi is known. See, for example, for example, A. Pandey, P. Selvakumar, C. R. Soccol, P. Nigam, “Solid state fermentation of the production of industrial enzymes”, Current Science, 1999, volume 77, no. 1, pages 149-162; and P. Cen, L. Xia, “Production of Cellulase by Solid-State Fermentation”, Advances in Biochemical Engineering/Biotechnology, 1999, volume 65, pages 69-92. However, there remains a need for improved methods and diverse organisms for culturing fungi on cellulosic solid supports to produce highly effective enzymes for use in the hydrolysis of diverse plant based lignocellulose. The need is particularly great for cellulosic supports rich in crystalline cellulose, which is difficult for Trichoderma and Aspergillus to degrade.